Materials that are capable of providing rheological properties including thickening to aqueous compositions find a variety of applications in cosmetic and pharmaceutical formulations, as well as other personal care products, in the form of creams, pastes, gels, ointments, and emulsions. Uses include hand creams, lipsticks, shampoos, hair conditioners and similar health and beauty aids. Such materials are also useful in textile printing inks, drilling muds, and aqueous coating compositions. Numerous rheological additives are currently employed throughout various industries, such as natural gums, for example, acacia, aliginate, carrageenan, guar, karaya, pectin, tragacanth, and xanthane; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and methyl hydroxypropyl cellulose; inorganic materials such as clays and fumed silica; and synthetic polymers such as acrylic acid based copolymers and polyoxypropylene/ethylene block polymers.
All of the prior art materials exhibit specific benefits and associated disadvantages for different aqueous systems. For example, two cellulose-derived substances that are widely employed are sodium carboxymethyl cellulose and nonionic hydroxyethyl cellulose. Both materials provide high thickening efficiency in water at low concentrations. However, these materials, and natural gums in general, are subject to biodegradation. Furthermore, although the cellulose derivatives provide excellent performance in terms of thickening, they do not impart to personal products in particular such features as superior feel and appearance that boost the consumer appeal for such products and provide customer satisfaction.
The use of synthetic polymers as rheological additives has become widespread throughout the health and personal care product marketplace due to their resistance to biodegradation and their ability to thicken personal care aqueous compositions with a smooth feel, smooth texture, and in certain instances, provide clear transparent gels. The most commonly employed synthetic polymers are lightly crosslinked carboxylic polymers prepared from unsaturated carboxylic acid containing monomers such as acrylic acid, methacrylic acid, and maleic anhydride. Some polymers of this type are described in U.S. Pat. No. 2,798,053. The high thickening efficiency of these polymers is achieved by crosslinking acrylic acid based polymers with a polyalkenyl polyether or polyhydric alcohol. The crosslinking renders the polymers water-swellable or water-dispersible.
Other known carboxylic polymers which maintain viscosities in aqueous solutions containing inorganic ions or salts are described in U.S. Pat. Nos. 3,915,921; 3,940,351; and 4,509,949. The copolymers consist of an unsaturated carboxylic acid monomer and one or more alkyl acrylate esters wherein the alkyl groups contain 10 to 30 carbon atoms and, optionally, a crosslinking monomer which is a polyfunctional vinylidene monomer containing at least two polymerizable CH.sub.2 =C&lt; groupings, the unsaturated bonds of the polymerizable groupings being non-conjugated with respect to each other.
Japanese Kokai 52-006789 discloses a water dispersible vinyl copolymer which is useful as a thickener in cosmetics and emulsions which is prepared by copolymerizing (meth)acrylic acid with triallylisocyanurate in the presence of a copolymerization catalyst.
U.S. Pat. No. 4,090,998, discloses crosslinked carboxyl-containing polymers which are water swellable in the form of their salts and are prepared by the polymerization of a monomeric mixture of maleic anhydride, indene, and a crosslinking monomer containing a plurality of CH.sub.2 =C&lt; groupings.
Processes for preparing the above described carboxylic polymers are described in U.S. Pat. Nos. 4,267,103 and 4,758,641.
U.S. Pat. No. 4,800,220 discloses crosslinked carboxylic copolymers for providing better resistance to viscosity losses in the presence of dissolved salts. Such copolymers are obtained by copolymerization of an unsaturated carboxylic monomer, a crosslinking agent, an acrylic or methacrylic ester with a polyalkylene glycol, and optionally, an alkyl acrylate or methacrylate.
U.S. Pat. Nos. 4,167,502; 4,138,381 and 4,230,844 disclose polymers of a polymerizable mixture which are useful as thickening and bodying agents when partially or completely neutralized in cosmetics, personal care products, latex paints, and oil well drilling compositions and which provide both good flow and leveling properties, as well as sag resistance to aqueous coating compositions.
U.S. Pat. No. 4,062,817 discloses carboxylic polymers comprising an unsaturated carboxylic acid, at least one alkyl acrylate or methacrylate ester in which the alkyl group contains 10 to 30 carbon atoms, and a second acrylate or methacrylate ester containing an alkyl group of from 1 to 9 carbon atoms, and optionally, a crosslinking monomer which is a polyfunctional vinylidene monomer containing at least two polymerizable CH.sub.2 =C&lt; groupings which rapidly absorb and retain large quantities of water and ionic fluids and are useful in disposable nonwoven articles. U.S. Pat. Nos. 4,668,731; 4,686,254; 4,778,737; 4,362,715; 3,953,591; and Canadian Pat. No. 1,067,411 describe the utilization of specific carboxylic copolymers as thickeners.
German patent DE 2,949,843 discloses a method for preparing carboxylic acid polymers in the presence of a polyvinyl pyrrolidinone polymer which acts as a protective colloid, said polymers being disclosed as useful as thickeners in the cosmetic and pharmaceutical fields. U.S. Pat. No. 3,931,085 teaches compositions useful for non-woven textile printing operations which comprise a synthetic resin, a water-soluble polymeric carboxylic thickener and a surfactant which is added to the synthetic resin composition without a crosslinker to create, enhance, or augment the triggering action which initiates the coagulation and precipitation of the synthetic resin. The patent discloses non-ionic surfactants which include ethoxylated compounds related to glycol esters of fatty acids. The use of certain ethoxylated surface-active agents in combination with specified carboxyl polymers is also shown in the art. See U.S. Pat. Nos. 4,375,533, 4,419,502 and 4,526,937.
The various carboxylic polymers described in the prior art are useful as thickeners for aqueous media and, in some cases, hydroalcoholic solvents. The maximum thickening ability of these polymers is attained upon neutralization of the carboxylic acid groups with a base such as ammonium hydroxide, sodium hydroxide, potassium hydroxide, or an amine. However, particularly in the field of cosmetic formulations, new thickeners are desired that are more efficient and are more easily dispersed, in combination with better feel and rub-up qualities, compared to prior art thickeners.